PHP function introduction—is_resource(): Check whether the variable is a resource

PHP function introduction—is_resource(): Check whether a variable is a resource

In PHP, is_resource() is a very useful function for Determine whether a variable is a resource type. Resource types are used in PHP to represent external resources, such as database connections, file handles, image resources, etc. This article will introduce the use of the is_resource() function in detail and demonstrate its practical application through code examples.

is_resource()The syntax of the function is as follows:

bool is_resource ( mixed $var )

Among them, $var represents the variable to be checked. This function returns a Boolean value, true indicates that the variable is a resource, false indicates that the variable is not a resource.

The following uses several specific examples to illustrate the usage of the is_resource() function.

1. Check whether the file handle variable is a resource

$file = fopen("data.txt", "r");
if (is_resource($file)) {
    echo "文件句柄为资源类型";
} else {
    echo "文件句柄不是资源类型";
}
fclose($file);

The above code first uses the fopen() function to open a file and returns the file handle Assign a value to variable $file. Then, check whether $file is a resource type through the is_resource() function. If it is a resource type, output "the file handle is a resource type"; otherwise, output "the file handle is not a resource type". Finally, use the fclose() function to close the file handle.

2. Check whether the database connection variable is a resource

$host = "localhost";
$user = "root";
$pass = "password";
$dbname = "test";

$conn = mysqli_connect($host, $user, $pass, $dbname);
if (is_resource($conn)) {
    echo "数据库连接为资源类型";
} else {
    echo "数据库连接不是资源类型";
}
mysqli_close($conn);

In the above code, first use the mysqli_connect() function to connect to the database and return the The database connection is assigned to variable $conn. Then, check whether $conn is a resource type through the is_resource() function. If it is a resource type, output "the database connection is a resource type"; otherwise, output "the database connection is not a resource type". Finally, use the mysqli_close() function to close the database connection.

3. Check whether the image resource variable is a resource

$width = 500;
$height = 300;
$image = imagecreatetruecolor($width, $height);

if (is_resource($image)) {
    echo "图像资源为资源类型";
} else {
    echo "图像资源不是资源类型";
}
imagedestroy($image);

In the above code, use the imagecreatetruecolor() function to create a true color with specified width and height image, and assign the returned image resource to the variable $image. Then, check whether $image is a resource type through the is_resource() function. If it is a resource type, output "Image resource is a resource type"; otherwise, output "Image resource is not a resource type". Finally, use the imagedestroy() function to destroy the image resource.

Through the above code examples, we can clearly understand the specific application scenarios of the is_resource() function when determining whether a variable is a resource type. When we need to operate external resources, we can use this function to ensure that the variables being operated are valid resources and avoid errors.

Summary:
In this article, we introduce the use of the PHP function is_resource() in detail, and demonstrate the practical application of this function in three situations through code examples. Through the is_resource() function, we can easily determine whether a variable is a resource type and perform corresponding processing as needed. I hope this article will be helpful to everyone in the process of PHP resource processing.

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